This invention relates to supplying power to a tool in a downhole environment. Measuring while drilling (MWD) and logging while drilling (LWD) tools typically require electrical power to function; accordingly, it is desirable to provide sufficient power to ensure proper operation and accurate data collection.
Such efforts are disclosed in U.S. Pat. No. 5,744,877 to Owens, which is herein incorporated by reference for all that it contains. Owens discloses a system for providing large quantities of power at a selected voltage to a downhole well tool. A conductor extends between a surface regulator and the well tool. The voltage is continuously measured downhole at the well tool, and a signal proportional to such downhole voltage is transmitted to the surface regulator. The power transmitted by the surface regulator to the conductor is increased or decreased depending on fluctuations in the tool requirements and the downhole voltage. The downhole voltage signal can be modulated through the conductor to the surface regulator or can be transmitted through another conductor.
U.S. Pat. No. 3,980,881 to Veach et al., which is herein incorporated by reference for all that it contains, discloses an improved well logging system utilizing a single conductor cable to provide power from surface equipment to a down hole subsurface unit and for simultaneously supplying current mode telemetry signals from one or more radiation detectors in the subsurface unit to the surface equipment. The surface equipment includes a power supply for the subsurface unit comprising a constant current source having a high output impedance connected to a series pass voltage regulator having a low output impedance. A switching mode voltage regulator is employed within the subsurface unit to compensate for variations in the voltage supplied to the subsurface unit which result from variations in cable resistance and other factors.
U.S. Pat. No. 4,806,928 to Veneruso, which is herein incorporated by reference for all that it contains, describes a downhole tool adapted to be coupled in a pipe string and positioned in a well that is provided with one or more electrical devices cooperatively arranged to receive power from surface power sources or to transmit and/or receive control or data signals from surface equipment. Inner and outer coil assemblies arranged on ferrite cores are arranged on the downhole tool and a suspension cable for electromagnetically coupling the electrical devices to the surface equipment is provided.